FreeStyle Libre experiences

Because I still haven’t been able to sort out the Dexcom/insurance situation, I asked my doctor to prescribe a FreeStyle Libre, thinking that if it wasn’t affordable enough, I could at least start learning how different foods/meds/doses impact my BG. I picked it up last night, inserted when I got home, and it finished the warmup this morning before breakfast.

I have a couple of questions - if you test a meter against a CGM, should you expect them to be close, even with the lag (provided your BG isn’t quickly rising/falling)? I use a ReliOn Prime from Walmart, so I’m not sure if the differences I’m seeing are entirely the Libre or a combination of both being off.

I can’t post pics currently, but here are the numbers I got:

ReliOn - 88
Libre - 61 (with slanted up arrow)

Since it said my BG was rising, I tested again in about 15 mins to see if it had leveled off:

ReliOn - 92
Libre - 75 (steady)

The Libre stayed between 73-76 while I was making breakfast. At 1hr post:

ReliOn - 136
Libre - 129

Any thoughts as to why the numbers would be further apart when lower, but pretty close as they get higher?


@Pianoplayer7008, we rely heavily on our CGM at all times. Yet, I have documented, and sometimes posted, multiple examples of cases where, for us, there will be a systematic error between the two. For instance, for us, after injecting for a meal and waiting until we have turned the corner, once my sons starts to eat there will ALWAYS be a significant difference btween the CGM and the BG meter, for at least 25 to 30 minutes, sometimes longer.

The differences come from at least two sources:

  • the CGM relies on interstitial fluid, while the BG meter uses streaming blood

  • the CGM algorithm is trying to estimate numbers, and makes adjustment calculations every read. These calculations actually lead to some errors when there is change in levels.

Here, likely, the BG is going up, so the Libre is lagging I am guessing

I am assuming that when you say “steady” it means a horizontal arrow. I find that these arrows are gross approximations of the actual curve. If you had a way to picture the curve in your head your eye would be able to estimate trends a lot better than the arrows. I am thinking that, here, the meter has still not caught up to the actual blood measurement, and is still climbing slowly.

By then, typically our CGM and our BG meter are reasonably in sync. Yours appears to be as well, and the residual difference can be due to either one of the two or both.

Btw, your ReliOn is not a bad meter! It is not as precise as the Contour One, but it is the best of the cheaper strip systems (check @MaryPat’s thread here: The best BG glucose meter that your insurance will pay for) so it is one that I would be happy to rely on.

All BG meters, of course, have some noise, so there is always a bit of jumping up and down in the data. If you are willing to spend about 50 strips to figure out exactly how it impacts you, I will post in the next few minutes a different thread that shows what you can do to know exactly what you are facing.

To my eye, your results are very good, and, in fact, better than I expected. This is a very good performance for a self-calibrated meter.

[EDIT] I posted a method to calculate your average BG meter error here: How to estimate your BG meter's noise

Thank you! I am pleased that it did finally match up. After seeing the other thread that showed the Libre reading consistently higher than the Dexcom, I was afraid it would be consistently off for me and just not worth the money.

I would comment on the “arrows” however the forum filter will not let me express my thoughts on this one.

As Michel mentions, I prefer to eyeball the graph and ignore the “lovely” arrow.


:rofl: I thought that would be a helpful feature - are they really that unreliable?

I would not characterize as unreliable. I believe Michel described it well.

It is more the arrow (IMHO) lags the cgm data which lags the blood BG. It is excessive lagging when eyeballing the graph appears to give a more realistic idea of data movement.

(BTW - in case not blatantly obvious, my experience is years with the Dexcom and zero with the Libre)


@Pianoplayer7008, I posted the procedure to figure out your BG noise here: How to estimate your BG meter's noise

I will also edit my original post in include the reference.

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I got stuck at the first line:

When you are stable around 70, take 15 consecutive BG measurements, using different fingers, every 30 seconds.

(I might not have gotten enough sleep as I can’t stop laughing)
Ok - gonna read the whole thing now…


OK, fine, I’ll reword it :slight_smile: You are giving me grief…


I thought maybe the Libre was just going to be useless for me under 100, as I checked it at 2hrs post breakfast and it said I was in the 60s (meter read 80s). When it kept dropping over the next 20 minutes, and I finally started feeling low symptoms, I checked meter again…

This does confirm that Afrezza/my pancreas is somehow dropping me low after it’s supposed to be wearing off.


The most likely culprit is your pancreas.


That’s what I think. It must’ve revived itself somewhat, which is causing me some grief. My lows are lower (for me) and take a bit more to come up now. :slightly_frowning_face: Oh, well. Took advantage of this one and had a bowl of cereal.


Have you had a quadruple treat low yet? They are infrequent but loads of fun. edit, almost as much fun as the “fake” low, where your treatment appears to work fro 15 minutes by rising on your CGM then dives back into low territory, again and again…


I tend to agree with @Chris for the likely cause, athough, of course, you never know for sure.

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No, I haven’t! The lowest I’ve seen on a meter for me is 52 (I think I was lower this time, but didn’t check when I was first treating - the Libre was stuck on LO for a bit though).

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The honeymoon was the least favorite part of diabetes for us, it lasted for about 8 months, and made all of the calculations and learning hard because every result had more variability than we thought it should. Once we got past that, doing the same thing usually resulted in a similar results and things made much more sense.


Things had been more consistent up until now - usually I would only get random “help” from my pancreas if I slightly overshot my target - 140-160s - and so I just wouldn’t correct then, but it never sent me low. I’m not a huge fan of this change, obviously.


@Pianoplayer7008, it occurs to me that your Freestyle Libre is lower than your ReliOn, despite the fact that the curve is going down, so this is not a lag issue.

It appears to me, based on your other numbers, that you might expect a slight bias towards lower numbers for this instance of your Freestyle Libre, as compared to your ReliOn meter. Of course, the sample of measurements is still low at this stage.

It might be worth your keeping a log of what your Libre was measuring every time you take a ReliOn fingerpoke, for the first week or so?

I plan to keep a log for sure - I’m curious to see if it keeps running lower and how I feel with those numbers. This morning when it first read in the 60s, I felt fine. I didn’t feel anything when I went low until it read in the 40s (meter was in 50s). I also didn’t feel my last low until I was in the 50s on my meter. I used to feel them in the 60s, but we will see if I have adjusted to being lower more often and now don’t feel them til they’re in the 50s.


Imho, this is dangerous. I think it was Terry who became largely hypo-unaware through such a drift until he retrained his body.

My suggestion to you is to aim at staying above 80 for a month or two. This way you will retrain your body to feel something below 65 or 70. Mo2c, of course.

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